Fastening devices for attaching reference devices to a part of a body for computer-assisted medical procedures are known. Such reference devices may be attached, for example, to a bone. The fastening devices may be configured in various different designs. Examples include clamps and/or forceps with pointed portions such as spikes that penetrate a body or bone when being fastened. Rod-shaped devices having screws that secure a reference device to a body or bone also are known, as well as plate shaped fastening devices that are fastened to a body or bone by a number of screws.
In the field of computer-assisted surgery, a reference device may be attached to each of various fastening devices. The reference device may be an array including markers that are used for navigation in computer-assisted operations. The markers can be active markers that emit radiation that is detected by a camera system in an operating room. The markers also can be passive markers such that they reflect radiation that is detected by a camera system in the operating room. If a surgeon chooses to use computer or navigational assistance in connection with a treatment tool to be navigated (for example, a surgical instrument) the surgeon may attach a reference device to the instrument. When the reference device of the instrument apparatus is detected by the camera system at the same time as the reference device of the body, the position of the instrument relative to the position of the body may be determined.
Operations that require a high level of precision are often performed with computer assistance. For this reason, it is important for the reference device to be securely fixed or attached to the bone or other body part. The fastening device for securing the reference device to the bone should not be inadvertently detached or broken and, thus, should be designed to withstand high mechanical stresses. For this reason, and for the reason that the devices should be reusable and sterilizable, conventional fastening devices are often made of high-grade steel or titanium.
Another characteristic of fastening devices is their size. Surgeons often desire a smaller fastening device so that it does not interfere with a computer-assisted operation. A smaller device does not obstruct the surgeon's freedom of movement and field of vision.
Operations requiring a high level of precision often may be accompanied by imaging methods, including intra-operative imaging. Accordingly, a recording may be taken (for example, using a CT scanner or an MRT scanner) during an operation, wherein it is important to obtain high-quality scan recordings. The use of certain fastening device materials may cause distortion or artifacts in the recordings. Metals are generally radio-opaque as well as some ceramics, whereas plastics are generally radio-translucent. Accordingly, conventional fastening devices made of high-grade steel and titanium alloys may cause numerous artifacts.
The imaging methods can be various types of x-ray recordings (two-dimensional x-rays, three-dimensional x-rays, or three-dimensional computer tomography). In this respect, it is noted that artifact formation in two-dimensional x-ray recordings is different than artifact formation in three-dimensional x-ray recordings that are compiled or reconstructed from various two-dimensional recordings. If materials are used that are radiolucent, such as plastics or certain ceramics, then good two-dimensional x-ray recordings (fluoroscopic recordings) can generally be obtained. The same does not apply to a three-dimensional image or two-dimensional recordings from which the three-dimensional image can be obtained. Artifacts can occur in these images even with materials having good radiolucent properties. It is noted that artifact creation is often not based on the density of the fastening device material but rather on differences in densities that occur in a body.